1. Field of the Invention
The present invention relates to an electrolyte system technology, and more particularly to a novel electrolyte system based on a supercritical fluid solvent using a variety of dissolved species.
Supercritical fluids possess properties that are a combination of gas and liquid and are defined by the critical point for temperature and pressure. Specifically, the critical temperature is that value at which additional pressure will not condense the fluid to a liquid and the critical pressure is the value above which additional heat will not vaporize the fluid to a gas. Supercritical fluids possess unique solvent properties useful in various chemical formulations or processes. Many common compounds (water, nitrogen, hydrocarbons, fluorocarbons, etc.) possess supercritical properties, but often at quite elevated pressures or temperatures.
One of the well-known and more useful supercritical solvents is carbon dioxide (31 degrees Celsius critical temperature and 73 atmosphere critical pressure). Numerous chemical extraction processes, polymer synthesis, tertiary oil recovery operations, microbiological/pharmaceutical applications, etc. employ supercritical carbon dioxide as a primary solvent or a key co-solvent. In the supercritical state carbon dioxide has a density starting at less than 0.5 gm/cc and is miscible with water and many other organic liquids. Certain hydrocarbon polymers, large fluorocarbons molecules and other organic compounds are often especially soluble and miscible in supercritical carbon dioxide, but inorganic salts are generally rather insoluble and will even precipitate out of aqueous solutions in the presence of supercritical carbon dioxide (SC CO2).
Unlike other common solvents used for electrolytes, SC CO2 is virtually inert, totally non-toxic and non-flammable. Unlike aqueous and organic liquid electrolyte solvents, carbon dioxide will not decompose, react with other typical electrochemical cell components, form gaseous reaction products or solid deposits or create other safety or performance problems. Electrochemical applications involving organic solvents, on the other hand, suffer severe service life reductions, electrical output performance limitations and various safety issues due in large part to the use of chemically and thermally unstable electrolyte solvents. A variety of modifications to the base technology are also possible. A supercritical fluid can be used alone or in combination with other supercritical fluids or aqueous or organic liquids to provide a range of properties and performance capabilities.
The use of supercritical fluids or near supercritical liquids (liquefied/densified gases) have now been identified as a new, unexplored opportunity to provide an improved electrochemical system. Such solvent systems provide voltage, thermal and chemical abuse tolerance beyond all conventional organic and aqueous solvents and many inorganic materials. The viscosity, density and solvating properties of the supercritical fluid solvent are also superior to many other known systems.
Current state-of-the-art ambient temperature lithium batteries have good overall performance, but are typically based on thermally unstable organic liquid solvent electrolyte solutions. Power fade and safety issues of baseline cells have been two of the biggest and most perplexing problems to this point for lithium batteries used at high voltages, charge/discharge rates and temperatures. Furthermore, as the sizes and battery voltages become larger and the demands for extended life increase, the issues of safety and impedance increases become more acute. The basic concept is to design high pressure cylindrical cells with the smallest cell diameter possible. For example, when the cell diameter is double, the wall thickness must increase proportionately to maintain the same safety margins. Therefore, small diameter stainless steel cylinders with less than an inch diameter can meet the pressure requirements of 100 atmospheres in a wall thickness of less than one millimeter.
The increased weight of these cell cans would only result in a small penalty to overall battery weight. If necessary, the stainless steel cell can may be replaced with a thin wall aluminum can to achieve a weight reduction. These type of trade-offs are shown in Table 1, where “SS” is stainless steel and “FRP” is fiber reinforced epoxy.
TABLE 1Cell Case Design ComparisonsCell Can MaterialCanCan WallPressureSafety(SS = 33 k psi yield,Diameter,Thickness,at Yield,Factor atFRP = 16 k psi yield)inchinchpsig100 atmCommentStainless Steel0.70.01514500.99typ. 18650 cellCynlindrical Cans(~4gm/cm len)10.02516841.1510gm/cm len10.05034382.3420gm/cm len20.05016841.1540gm/cm len20.10034382.3480gm/cm len40.10016841.15160gm/cm len40.20034382.34320gm/cm lenCarbon Fiber/Epoxy10.05016671.135gm/cm lenReinforced Cans20.10016671.1320gm/cm len40.20016671.1380gm/cm len
Prior technology utilizing supercritical fluid electrolytes has been limited to cover simple oxidation/reduction reactions at an electrode surface and do not suggest or allow for the transport of ions between electrodes. Furthermore, there has been no application for the use of supercritical fluid in an energy storage and energy production device where faradic, capacitive reactions must occur.
2. Description of the Related Art
United States Pat. App. No. 2005029117 to Patricia A. Mabrouk, deals with the electrochemical synthesis of electrically conductive polymers in supercritical fluids, for example supercritical CO2. The use of the supercritical fluid as a solvent results in the reduction or elimination of hazardous reagents and environmentally hazardous waste, which was generated in the prior chemical synthesis techniques. The electrochemical approach eliminates the need to add a charge transfer agent as the electrode serves this purpose. The resulting polymers are characterized by high conductivities and distinctive surface morphology, which suggests that they may be more appropriate than the previous materials for certain applications (e.g., corrosion inhibition, optical applications, etc.).
United States Pat. App. No. 20030019756 to Hideo Yoshida; et al., deals with a novel method of electrochemical treatment such as electroplating, etc. and an electrochemical reaction apparatus thereof which is high in reactability and able to be electrochemically reacted efficiently, which is small or zero in amount of generation of liquid waste such as electrolytic solution and cleaning liquid and therefore amicable to the environment, and in which it is no more required to clean the electrode, etc. with cleaning liquid after reaction. Electrochemical reaction is executed in a reaction vessel (6) containing matter (5) which is in a supercritical or subcritical state and an electrolytic solution (1), and after reaction, the supercritical or subcritical matter (5) is shifted into a state of the matter (5) before being shifted into a critical state.
While these units may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.